1. Field of the Invention
The present invention relates to an actuator apparatus that adjusts optical properties of an objective optical system, and an image pickup unit that are arranged in an endoscope.
2. Description of the Related Art
As is known, electronic endoscopes are widely used for observing and/or treating the inside of (body cavities of) living organisms or for examining and/or repairing the inside of industrial plant facilities and the like. In recent years, in some electronic endoscopes an image pickup unit is used that can change a focal length for a focusing function that adjusts a focus of a photographing object or a zooming function that implements wide zooming/telescopic zooming by moving an observation optical system in the direction of the photographing optical axis.
This kind of technology that moves a movable lens frame to adjust optical properties for a zooming function or the like in an image pickup unit provided in an endoscope is disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2007-229155.
The aforementioned Japanese Patent Application Laid-Open Publication No. 2007-229155 discloses technology of an endoscope that utilizes an urging spring and a shape memory alloy (hereunder, referred to as “SMA”) wire as an actuator apparatus for moving forward and backward a movable lens frame that retains a movable lens for adjusting the optical properties.
According to this conventional image pickup unit of an endoscope, the movable lens frame is moved backward against the urging force of the urging spring when the SMA wire is caused to contract by passing a current thereto. Further, when the current being passed to the contracted SMA wire is stopped to cause the SMA wire to expand, the movable lens frame is moved forward by the urging force of the urging spring. In this manner, an optical property such as a zooming function is adjusted.